Speed reducer

ABSTRACT

A speed reduction planetary transmission comprises an input sun gear, a series of planet gears meshing with the sun gear and a fixed ring gear, and an output ring gear. The number of teeth on the two ring gears differs by a very small number. The planets are free-floating and constructed to resiliently yield along their diametral dimension, to permit assembly in spite of an intentional interference fit between the gears. This eliminates backlash and distributes the load equally among all the planets. A modified embodiment utilizes a stepped planet gear, part of which meshes with an idler sun gear.

United States Patent Duggar, Jr. [4 1 July 11, 1972 [54] SPEED REDUCERFOREIGN PATENTS 0R APPLICATIONS [72] Inventor: Anderson Duggar, Jr.,4350 Delemere 925,687 5/1963 GreatBritain...........................74l80l Blvd., Royal Oak, Mich. 48073804,223 I 1/1958 Great Britain...

[22] Filed: 1970 Primary Examiner-Carlton R. Croyle [21 Appl. No.:79,817 Assistant Examiner-Thomas C. Perry Attorney-Cullen, Settle.Sloman 8t Cantor [52] US. Cl ..74/801 57 ABSTRACT [51] Int. Cl ..Fl6h1/36 v I 53 Field olSeareh ..74 so1 A l reducuon Planetary compnm an psun gear, a series of planet gears meshing with the sun gear 56]References u and a fixed ring gear, and an output ring gear. The numberof teeth on the two ring gears difi'ers by a very small number. TheUNITED STATES PATENTS planets are free-floating and constructed toresiliently yield along their diametral dimension, to permit assembly inspite of 3,453,906 7/1969 JUnklChl ..74/801 an intentional interferencefi between the gem This 2,456,814 12/1948 Church ..74/801 X eliminawsbacklash and distributes he load equally among n 476,101 5/1892 Thomson..74/801 the planets A modified embodiment utilizes a stepped planet 33/ 1963 gear, part of which meshes with an idler sun gear. 3,218,88911/1965 Jarchow.. 3,421.390 1/1969 Lohr SClalllngDraWlltgHguMPKTENTEDJBL 11 I972 3. 675.51 0

INVENTOR ANDERSJN DUGGAR JR. BY

CULLEN, SETTLE, SLOMAN B CANTOR. ATT'YS.

SPEED REDUCER BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a cross-sectionalelevation through a planetary gear type of speed-reducing transmission.

FIG. 2 is an end view of a typical planet gear shown in FIG. I, and

FIG. 3 is an end view, similar to FIG. 2, but showing a modified planetgear.

FIG. 4 is a view similar to FIG. I, but showing a modified form of theinvention.

DETAILED DESCRIPTION OF THE INVENTION A high speed ratio type ofplanetary gear transmission is illustrated in FIG. 1. Generally, thistransmission comprises a housing having an input sun gear 12, a fixedring gear 14 formed integrally with the housing 10, a series of planetgears 16 (only one of which is illustrated) in mesh with sun gear 12 andring gear 14, and an output ring gear 18 also in mesh with an axiallyextended portion of planet gear 16. While only one planet gear 16 isshown, it is understood that a plurality of such gears may becircumferentially spaced about sun gear 12, as is common. If more thanone planet gear is used, it will be necessary to make allowance for thedifferent number of teeth on the two ring gears. One method is to formeach excess planet gear with two distinct longitudinally spaced gearportions, each identical but angularly indexed slightly relative to eachother. Another method is to physically separate each excess planet gearinto two unconnected parts, and permit them to find their own meshinglocation. The choice of these methods is governed by bearing loads,number of teeth, and so forth, as will be understood by those skilled inthe art.

As is well known in high ratio planetary transmissions of this type, ifthe number of teeth on ring gear 14 differs by a very small number fromthe number of teeth on ring gear 18, then ring gear l8 will rotate at anextremely low angular velocity relative to that of input sun gear 12.This is so because as planet gear I6 walks around the interior ofstationary ring gear 14, it will cause output ring gear 18 to rotatethrough an are approximately equal to the difference in the number ofteeth between the two ring gears for each revolution of planet gear 16about sun gear 12. For example, if fixed ring gear M has I teeth, ringgear 18 119 teeth and sun gear l2 l2 teeth, then the ring gear 18 willmake one revolution for every 1309 revolutions of input sun gear 12.

The present invention relates to means for improving the compactness andload carrying capacity of transmissions of this general type, whilereducing the backlash. The first factor which contributes to theachievement of these objectives is free-floating planet gears 16. Thatis, they are not mounted on a spider or carrier member. This means thatthey are self-centering and will seek their own proper meshing positionamong the sun and ring gears.

Secondly, the gear elements are dimensioned so as to require a slightinterference lit at the time of assembly. To facilitate such assembly,notwithstanding the interference fit, planet gears 16 are preferablymade so as to be resiliently yieldable along their diameters. This canbe accomplished by making each of planet gears 16 in the form of athin-walled annulus as shown in FIG. 2. Alternatively, the planet gearscould be made of a semi-resilient or elastic material. Either of thesealternatives would permit planet gears 16 to yield or flex at the timethey were forceably inserted into mesh between sun gears l2 and ringgears 14 and 18. By this means, planet gears 16 automatically float orshift into a position in the gear set whereby the loads are equalizedamong the teeth of each of the planet gears. The absence of a spider orcarrier member, along with the yieldability of the planet gears, assuresthat planet gears 16 will shift to the position that produces thisresult. This combination of factors also substantially eliminatesbacklash.

To achieve the necessary degree of flexing at the time of assembly, itmay become necessary to reduce the wall thickness of annular planetgears 16 to a point where the strength of the gear would be inadequateto prevent its deflection entirely out of mesh with the ring or sungears under high torque load conditions. For this purpose it may bedesirable in some circum' stances to reinforce the annular planet gearsfor their load carrying function, while permitting adequate flexingduring assembly, by inserting a solid non-compressible plug 24 (as shownin FIG. 3) within annular planets 16. By making the diameter of plug 24a predetermined amount smaller than the internal diameter of annularplanet 16, an annular gap would exist between these two elements toaccommodate a predetermined degree of diametral flexing or distortionduring assembly, while limiting the ultimate degree of distortion ofplanet 16 under high load conditions. Alternatively to using anon-compressible plug, a plug having a desired controlledcompressibility could be employed.

The above described transmission lends itself especially well to compacthigh speed reduction units. Where compactness is essential, it becomesdesirable to eliminate the additional diametral dimension necessitatedby bearings. This invention permits much higher loads to be carriedwithout the need for separate bearing elements. Most importantly, thefree-floating and flexing features of the planet gears distribute theload equally among the planets, thus reducing the peak loads ofteninduced in conventional unequally loaded planet gears. Secondly, byusing a ring gear as the low-speed high-torque output member, the toothload is reduced since the high torque occurs at maximum diameter.

As illustrated, no bearing elements are employed. For higher loads,surfaces 20, 22 and 24 could be employed as bearing surfaces, orseparate bearing elements could be inserted at those locations.

A modified form of the invention is illustrated in FIG. 4. Thistransmission comprises a housing 26 having an input sun gear 28, a fixedring gear 30 fonned integrally with housing 26, an output ring gear 32,an idler sun gear 34 freely rotatable on an extension of the input sungear shaft, and a stepped planet gear 36. A first gear portion 38 ofplanet gear 36 meshes with sun 28 and ring 30, while the second smallerportion 40 meshes with sun 34 and ring 32. As described above regardingplanet 16, planet gear 36 is also of thin-walled annular construction,either with or without a reinforcing plug, to achieve the desiredresilience.

An exemplary form of the FIG. 4 embodiment would employ the followingnumbers of teeth: l2 teeth on sun 28, I5 teeth on sun 34, 54 teeth onplanet 38, 5| teeth on planet 40, I20 teeth on ring 30, and 117 teeth onring 32. This would yield a gear ratio of 35 l l.

The configuration of FIG. 4 provides another method of allowing for theproblem of meshing with two different sized ring gears. The idling sungear 34 merely takes up the radial forces from planet 40.

While only two gear configurations have been illustrated it is to beunderstood that other layouts could be used without departing from thespirit of this invention. For example, higher ratios could be obtainedby adding further gear sets in series so that ring gear 18 would be theinput member for an additional gear set.

I new claim:

1. In a planetary gear type speed-reducing transmission characterized byan input sun gear, a fixed non-rotatable ring gear, at least onefree-floating planet gear engaging said sun and fixed ring gears to bedriven by said sun gear and unsupported by any planet gear carriermember, and a rotatable ring gear engaging said planet gears to bedriven thereby, the transmission containing no carrier-supported planetgears, the numbers of teeth on said two ring gears differing by a verysmall number so that a high speed reduction ratio is created betweensaid input sun gear and said rotatable ring gear, the improved method ofincreasing the load carrying capacity while reducing backlash in thetransmission which comprises the steps of:

forming said gears to relative diametral dimensions resulting in aslight interference fit at the time of assembly; and

fabricating said planet gears in suc'h a manner that their diametraldimensions are resiliently yieldable within the range of forcesencountered in overcoming the interference fit at the time of initialassembly of the transmisslon; whereby the deflection of said planetgears required for assembly of the transmission coupled with thefree-floating mounting of said planet gears produces a tightly meshingtransmission wherein the loads are distributed equally among all thesaid planet gears and wherein backlash is substantially eliminated. 2.The transmission of claim 1 wherein the resilient yieldability of saidplanet gears is achieved by forming each planet gear as a thin-walledannulus.

3. The transmission of claim I wherein the resilient yieldability ofsaid planet gears is achieved by forming each planet gear of a resilientmaterial.

4. The transmission of claim 2 wherein a reinforcing central plug isinserted within the bore of each of said annular planet gears, with apredetemtined radial gap between said plug and its associated planetgear, to limit the extent of the flexing of said planet gears.

5. The transmission of claim 1 wherein said planet gears are stepped soas to have two distinct gear portions of appropriate diameters formeshing with the fixed and rotatable ring gears.

1. In a planetary gear type speed-reducing transmission characterized byan input sun gear, a fixed non-rotatable ring gear, at least onefree-floating planet gear engaging said sun and fixed ring gears to bedriven by said sun gear and unsupported by any planet gear carriermember, and a rotatable ring gear engaging said planet gears to bedriven thereby, the transmission containing no carrier-supported planetgears, the numbers of teeth on said two ring gears differing by a verysmall number so that a high speed reduction ratio is created betweensaid input sun gear and said rotatable ring gear, the improved method ofincreasing the load carrying capacity while reducing backlash in thetransmission which comprises the steps of: forming said gears torelative diametral dimensions resulting in a slight interference fit atthe time of assembly; and fabricating said planet gears in such a mannerthat their diametral dimensions are resiliently yieldable within therange of forces encountered in overcoming the interference fit at thetime of initial assembly of the transmission; whereby the deflection ofsaid planet gears required for assembly of the transmission coupled withthe free-floating mounting of said planet gears produces a tightlymeshing transmission wherein the loads are distributed equally among allthe said planet gears and wherein backlash is substantially eliminated.2. The transmission of claim 1 wherein the resilient yieldability ofsaid planet gears is achieved by forming each planet gear as athin-walled annulus.
 3. The transmission of claim 1 wherein theresilient yieldability of said planet gears is achieved by forming eachplanet gear of a resilient material.
 4. The transmission of claim 2wherein a reinforcing central plug is inserted within the bore of eachof said annular planet gears, with a predetermined radial gap betweensaid plug and its associated planet gear, to limit the extent of theflexing of said planet gears.
 5. The transmission of claim 1 whereinsaid planet gears are stepped so as to have two distinct gear portionsof appropriate diameters for meshing with the fixed and rotatable ringgears.